Control system



Dec. 16, 1952 A. J. HORNFECK CONTROL SYSTEM 6 Sheets-Sheet 1 Original Filed J1me 6, 1946 modzmDm IQEHIP INVENTOR. ANTHONY J. HORNFECK E JOmkZOO mOPOZ Dec. 16, 1952 A. J. HORNFECK 2,622,237

CONTROL SYQTEM Original Filed June 6, 1946 6 Sheets-Sheet 2 ONE CYCLE OF CAM 6 lN-FHASE OUT-OF-PHASE VOLTAGE ENVELOPE Sp SET AT 50% Sb SET AT MAX.

FIG. 2

HOFFHTIME +HONNTIME OF HEATER l3 \N-PHASE OUT'OF'PHASE LNVENTUR ANTHONY J.HORNFECK FIG. 3 Y

16, 1952 A. J. I-I-IORNFECK 2,622,237

CONTROL SYSTEM Original Filed June 6, 1946 6 Sheets-Sheet 3 ONE CYCLE OF ARM 66 -z;-i

lN-PHASE OUT-OF-PHASE VOLTAGE ENVELOPE s SET AT 50 FIG. 2A

4 JNVENTOR.

ANTHONY J. HORNFECK Dec. 16, 1952 A. J. HORNFECK CONTROL SYSTEM 6 Sheets-Sheet 4 Original Filed June 6, 1946 JNVENTOR.

ANTHONY J, HORNFECK m @mm m 33%. 92058 6 mokoz Dec. 16, 1952 v A. J. HORNFECK 7 I CONTROL SYSTEM Original Filed June s, 1946 s Sheecls-Sheet 5 MODULATOR BRIDGE l I RESET v k V RS RM 3 N CONTROL BRIDGE mmvrok.

ANTHONY J. HORNFECK BY Fla; 6 (w 1- Dec. 16, 1952 A. J. HORNFECK CONTROL SYSTEM Original Filed June 6, 1946 6 Sheets-Sheet 6 I CONTROLLER NO.

INVENTOR.

ANTHONY Jv HORNFEGK BY q A \NEY FIG. 7

MOTOR OF FIG, 6

. QQ R TO ADDITIONAL CONTROLLERS MQTOR OF.

FIG. 5

Patented Dec. 16, 1952 v 2,622,237 CONTROL SYSTEM.

Anthony J. Hornfeck, Lyndhurst, Ohio, assignor to Bailey Meter Company, a corporation of Delaware Original application June 6, 1946, Serial No.

674,752, now Patent No. 2,495,844, dated January31, 1950. Divided and this application July 15, 1949, Serial No. 104,870

My invention relates to eiectrical control circuits and particularly to electrical control circuits utilizing a measurement of a variable quantity, quality, position, or the like as the motivating'basis for a control or the same or of another variable. :A condition, quantity, quality, position or other variable which may be represented by anelectrical value such as resistance, Potential or other electrical characteristic may be continuously and instantaneously measured through the agency of the circuit to be described. The measurementso obtained may be used to effect a control of the same or of another variable which may or may not contribute to the magnitude or change in magnitude of the variable being measured.

Representative of variable quantities, conditions and the like to which my invention is directed are such variables as rate of fluid flow, temperature, liquid level, pressure; although the variable may equally as well be the position in space of an object, the throttling position of a valve, or the like. v

In the control or combustion or of other processes the time of response (process lag) of the system to a corrective change in.the rate of application of an agent, following a departure of the controlled condition from itsdesired value, depends on various constructional and operating factors. Over-travel, hunting, or the like of a control system results in inefficiency, waste and excessive wear on equipment. To satisfactorily control the operation of different processes and apparatus, several basic types of control are known and are Widely used in pneumatic and hydraulic control systems. A principal object of my present invention is the embodiment in electrical and electronic circuits of the proven desirable featuresof control readily adapted to a wide variety of process systems to be controlled.

Byway of example only, I have chosen to illustrate and describe my invention as applied to an electrically heated furnace wherein it is desired to maintain a uniform preselected temperature. It will be understood that such example is representative of a variable condition to be controlled through the application of an agent affecting the condition and is not to be taken as limiting.

The type of apparatus to be controlled frequently dictates the nature of the control which may be economically applied. In the control art ztwo' general types of control are recognized which :are referred to as on-off and modulating." .In on-oil control the controlled element, such 9 Claims. (Cl. 323-73) as a fuel supply valve, forexample, is in either open or shut position; or an electric heating resistor is turned on or on by a contactor. In modulating control the valve ispositioned between its extremes of travel to modulate or throttle the rate of flow of fuel through the valve. A modulating control, while preferable, is usually a more elaborate and expensive type and is not readily applicable to controlled elements which have only two possible positions, such as a solenoid operated valve which has only an open and a shut position, or an electric heating resistor element to which the current is either on or off. Such"on-ofi control is, however, at one or the other of two extremes and may lead to bad cycling.

So long as temperature is above standard, current to the furnace heating resistors is turned to off. If the temperature is at or below standard, the cur-rent is turned on. Obviously the full heating efiect of the resistor may be greater than is necessary to balance heat input to heat output for maintaining a uniform desired temperature. Preferably the amount of correction to rate of heat input should bear a relation to the extent of departure of temperature from standard. Modulating or throttling control tends to maintain the application of the corrective agent in accordance with the demand.

It is aparticular object of my present invention'to provide a controller for an on-off type of controllable apparatus embodying or incorporating the advantageous features of a mod-v ulating type of control. Basically, this result is accomplished by varying the proportion of on time to the off-time, giving the effect of a modulation related to the extent of departure of temperature from standard, and therefore to the actual value of temperature in relation to the standard value. v

In the drawings: V

Fig. lis a measuring and control system in connection With a resistance thermometer. L

Figs. 2,2A and. 3 aregraphs of electrical characteristics in connection with Figs. 1 and l. I

Fig. 4 illustrates a modification of a portion only of Figl. V

Fig. 5 is a modification of Eig; l. Fig. dis a circuit'diagram of of ap'artofFig.1. v

Fig. 7 is a diagram comparing theoperation of the motors of Figs. 5 and6.

Fig. illustrates how the circuit of Fig- 1 may be pluralized; l

All of the figures o the drawing are shown in a modification quite diagrammatic or schematic manner. In Fig. 1 I have shown the amplifier and motor control circuit in detail. I have not felt it necessary to duplicate these details in other figures which illustrate modification of a portion only of the complete circuit in Fig. 1.

Referring now in particular to Fig. 1, I indicate at I a phase sensitive A.-C. bridge having fixed resistor arms 2, 3 and 4. The fourth arm 5 of the bridge I is a resistance element located in an electric furnace 6 and sensitive to the temperature thereof. For balancing the bridge I provide an adjustable resistance I inserted between the arms 3 and 4 and providedwith a movable contact arm 8 for proportioning the resistance 1 between the arms 3 and 4.

For positioning the contact arm 8 I provide a motor 9 which also positions an indicator l relative to a scale I I and relative to a revoluble chart I2, thereby providing an instantaneous indication, as well as a continuous record, of the value of temperature to which the resistance arm 5 is sensitive.

The electric furnace 6 is preferably heated by an electric resistance element I3 receiving cur-- rent, from an A.-G. source M which also provides alternating current to the bridge I through a transformer I5.

Preferably the bridge arm 5 is a platinum resistance measuring element. The conjugate corners of thebridge I are connected'to an amplifier I6 and motor control I! for the motor 9. For an understanding of the phase sensitive A.-C. bridge for measuring the resistance of the leg 5 subjected to temperature of the furnace 6, reference may be had to the Ryder Patents 2,275,317 and. 2,333,393. The voltage output of the bridge I, supplied to the amplifier l6, assumes a balance or unbalance and a phase relation relative to the supply voltage dependent upon the magnitude and sense of the unbalance condition of the bridge. The amplifier I6 selectively controls motortubes I8, I9 which in turn control the amount and direction of unbalance of saturable core reactors 29 and 2| for directional and speed control of the motor 9 adapted to position the arms 8 and I0.

The motor 9 is of an A.-C. type having windings 22 and 23 ninety electrical degrees apart and also having a capacitor 24. When alternating current passes directly through one of the Windlugs and simultaneously through the other winding in series with the capacitor, the motor rotates in predetermined direction and at a speed determined by the extent of unbalance of the saturable core reactors 20, M. It is not necessary to go into greater detail as to the construction and operation of the amplifier I6 and the motor control circuit I I as reference may be had to the above mentioned Ryder patents.

In my present invention, in addition to providing an instantaneous indication and a con tinuous record of the value of temperature to which the arm 5 is subjected, I provide an electrical control of the heat input of the resistor I3 to the electric furnace 6. I have shown in this connection a power controller 25 which forms no part of the present invention. This may be any adaptable power controller for the resistance I3. My present invention resides in an electrical system intermediate the measuring system and the power controller, sensitive to the measuring system, and for turning on and off the power controller 25. Thus, upon departure of temperature within the furnace 6 from that which is desired,

the power controller 25 is turned on or off to increase or decrease the heat of the furnace tending to return the departed temperature to its desired value. The actual temperature is continuously indicated on the scale II and recorded on the chart I2.

The motor 9, in addition to positioning the contact arm 8 simultaneously positions the contact arm 21 over a slidewire 28. At 29 I indicate a contact arm adapted to be manually positioned along a slidewire 30 for establishing the temperature standard or control point to which the control works, i. e. the temperature value which is desired to be maintained at the sensitive arm 5.

The elements 21, 29, 29 and 30 comprise what I term a balanceable control network including the joining conductors 3I, 32. This circuit is supplied with alternating current power through the secondary winding 33 of a transformer 34. Contact arm 21 is positioned relative to the slidewire 28 by the motor 9 representative of actual temperature to which the resistance arm 5 is sensitive. Contact arm 29 is positioned relative to slidewire 30 manually to a point representing the desired temperature. The control circuit including these elements then establishes a signal so across the terminals 35, 36 of reversable phase and having a magnitude proportional to the unbalance of the control circuit.

The operation is as follows. If temperature within the furnace deviates from the desired value, then the resistance of the bridge arm 5 changes, causing an unbalance of the bridge I in one direction or the other dependent upon whether the actual temperature is above or below the desired temperature. The phase and magnitude of the A.-C. output of the bridge I follows the sense and amount of unbalance of the bridge and is applied to the amplifier I6 for control of the motor 9. Motor 9 rotates in predetermined direction and amount determined by the phase and amount of unbalance of the bridge I and positions the contact 8 along the slidewire I in proper direction to rebalance the bridge. The amount of movement of the contact 9 over the slidewire I to bring about such a rebalancing is representative of the deviation of the actual temperature from the desired temperature, and therefore the indicator I9 continuously shows on the index II and chart I2 the actual temperature of the furnace.

At the same time the motor 9 has positioned the contact 21 along the slidewire 28 in consoname with the departure of the temperature from the desired temperature. With such movement of the contact arm 2! the control bridge, including theeiements 21, 28, 29, 39, BI and 32 becomes unbalanced and an electrical value e0 is established across the terminals 35, 35 representative of the direction and extent of such unbalance. Such signal is effective to actuate the relay 26 controlling the resistor I3 through the agency of power controller 25 in a direction to return the temperature of the furnace toward the desired standard.

As the temperature (due to a change in heating of the resistor I3) returns toward desired value, the consequent temperature change at the resistance 5 unbalances the bridge I and causes the motor 9 to position the contacts 8 and 21 in proper direction and amount until the measuring bridge I and the control bridge are again balanced. It is appreciated, of course, that this action may be more or less continuous, i. e. that before the temperature returns completely to its desired standard there may be other influences acting. upon the furnace to prevent or to accelerate the return of the temperature to the desired value. L, Inother words, the measuring circuit is continuously indicating theinstantaneous tem-.

perature of the furnace and the control circuit is continuously regulating the power controller to maintain the temperature at the desired value or standard. I will now describe theoperation of the apparatus within the dotted enclosure 26 which I term an electronic relay. Such apparatus is under the control of the. signal e0 for regulating the power controller 25. 3

I have indicated as es the unbalance potential which may exist between the contact arms 21 and 29 of the controlbridge and which unbalance voltagernay be of a phase and magnitude depending upon the direction and extent of unbalance. In describing the'operation, I am considering that 80:60. In other words, for. the present I consider that 'the unbalance 6c is'applied' directly. to the terminals 35, 35.

The magnitude of the control impulse 60 is pr0- portional to the deviation of the measured quantity from thecontrol setting. The sense of the unbalance depends on whether the deviation is below or above the control setting, and determines the phase or polarity of the control impulse. This impulse is amplified or applied directly to the controller. troller operates to restore themeasured quantity to standard is determined by the phaseor polarity of the unbalance of the control bridge. A phase discriminatory device 31. is shown as a single envelope tube containing triodes 38 and 39 of which 39 is a rectifier whose function is to supply a reference D,-C. voltage E2 for 38. The voltage coat terminals 35, 36 is .impressedbetween the ridf40 and the cathode H of triode 38 establishinga D.,-C. voltage E1 to be compared to E2.

When the control bridge is in balance (cc o), i. e. when temperature (as represented bythe relative position of 21, 28) is at the desired value (as represented by the relative position of 29, triode '38 conducts a-predetermined amount of current resulting in a voltage drop E1. An adjustable contact 42 is manually positioned along a resistance 43 until E2 is slightly less than The voltage difference between E1 and E2 is then applied to thegrid 44 of a gas. filled tube 45, such as'a thyratron, through a resistor 46 and a capacitor' i'i. The negative voltage thus applied to the grid of the thyratron 45 is just large enough to prevent 45 from firing.

Inasmuch as the relay 26 being described provides anon-off control of the heating element 13, it will be appreciated that Idesire to fire tube 45 andenergize the mechanical relay 49 forthe power controller 25 only when the temperature tendsto fall below thede'sired standard value.

When the temperature increases abovestandard ordesired value the tube 45 does not fire orconduct. .'Ihe unbalance voltage at, on an increase in temperature above the desired value, isin phase with the plate voltage of triode 38 andgive's an increase in plate current over balance condi- 36 is supplied to the grid v of discriminator tri- Such voltage is out of phase with'the ode 38. plate voltage of 38 so that the plate current is reduced and E1 becomes less than is balanced by The direction in which the con- E2. This reduces the negative voltage applied to the grid of thyratron which fires, completing the circuit to energize relay 49.

Thus the relay 26 is sensitive to the phase of the voltage '60 or to the direction of unbalance of the control bridge, which is the same as saying that the relay 26 issensitive and responsive to a departure of actual temperature above or below the desired value of temperature. The system so far described comprises an on-off control. When temperature decreases belowthe desired value, then the thyratron 45 is fired, the relay 49 is energized and the power controller 25 is so activated as to increase the heat applied to the furnace 6 so that the actual temperature affective at 5 will be raised toward the desired value. If the temperature increases above the desired'value the control bridge becomes unbalanced in opposite sense, applying a voltage cc of opposite phase to the relay circuit 26, thereby shutting off the thyratron 45 to shut off the heat applied to the furnace 6.

The control point as it is sometimes termed in this art is the desired or standard temperature value indicated on a scale 50 by hand ad-- justment of the contact pointer 29 along the slidewire resistance 30. g

I will now describe the particular feature of my present invention wherein the proportion of on-time to off-time may be varied automatically to include in a basic on-oil control system certain advantageous features of the modulating type of control systems. I accomplish this by modifying the control bridge unbalance signal 6:: by a modulating signal mto the end that the signal e0 applied to the terminals 35, 36 is equal to eciem.

Basically the system consists of introducing a periodically cycling signal em in series or superimposed with the signal 6c obtained from a de viation of a control variable from standard. The result signal 60 is applied either directly or through the medium of an amplifier or electronic relay to operate an on-oif controller, such as an electric contactor, solenoid valve, or the like.

The superimposed signal cm is the unbalance voltage of a modulating bridge including an adiustable resistance element Sp and the secondary winding 54, of a movable core transformer 56. The movable core transformer 56 has an alternating current energized primary winding 51 variably coupled to the secondaries 54, 55 by means of a movable magnetic'core member 58, which is slowly reciprocated back and forth across a central coupling relation with the windings 51, 54 and 55.

For cyclically positioning the core 58 I provide linkage 59 having a roller arm 60 riding an eccentric disc or cam 6i driven synchronously by a motor-62. The shapeof the cam BI is relatively immaterial and may be provided with.

terposed, in the conductor is a resistance' Sb across which the unbalance voltage cm is taken in variable amount manually adjustable.

The magnetic core 58 is synchronously reciprojcated at a slow frequency by the motor 62. Preferably, this is about one complete cycle per minute, although the minimum frequency should be several times as great as the natural frequency of hunting of the control system. The core is symmetrical about the center of the asseinbly of windings 54, 55, 57 so that when the position adjustment S is at 50%, or mid-point, the unbalance voltage em will build up to maximum and decay to zero, first in phase and then out of phase with the supply voltage, which latter is the same as the plate voltage of the relay tube 38. 7

Under this condition and with the control bridge 21, 28, 29, 30, 3| and 32 perfectly balanced i. e; 80:0, the relay 59 will be on exactly half the time. A deviation in the measured variable (temperature) from the standard desired will produce a control voltage 60 alternately in phase and out of phase with the superimposed periodic signal em. As a result the ratio of duration of the in phase to the out of phase signal is modified by the magnitude and phase of ac. Hence if the controlled variable (temperature) is down from standard the on period of the relay 49 will increase in proportion to the magnitude of the deviation.

Fig. 2 depicts a typical voltage envelope for the signal em for one complete cycle of the cam 6|, i. e. for one complete reciprocation cycle of the core 58 coupling the energized primary winding 51 with the aiding secondary windings 54,

from neutral (A toward B in Fig. 2) a sixty cycle alternating current voltage em is developed, growing at a uniform rate from zero at A to a maximum at B, and of one phase which I designate as in-phase. As the core reverses its direction of motion and moves back toward neutral position the in-phase voltage em decays to zero (B to C). It will be appreciated that the curves drawn within the envelope A.BC' of Fig. 2 are representative only and are a part only of the eighteen hundred alternations occuring in the one-half minute half cycle of cam BI.

As the core 58 passes the neutral point the signal cm passes through zero in magnitude (C) and reverses in phase producing an out of phase signal of magnitude growing along C-D and decaying along D-E to zero. values depend upon different circumstances, I may say that the maximum value of the signal cl will be about 2 volts while the effective value of the signal the R. M. S.) will usually be about one volt under the conditions of Sp set mid-point and Sb set at MAX. These are the conditions indicated as a premise for Fig. 2.

Fig. 2A is similar to Fig. 2 in depicting a volt age envelope but it shows the voltage envelope developed by the arrangement of Fig. 4. Thus the horizontal dimension of the diagrammatic envelope is for a cycle of an arm GS later to be referred to. The purpose of Fig. 2A is to show that the same general nature of voltage envelope is developed with the embodiment of Fig. 4 as I have just explained is developed through the embodiment of Fig. 1.

As clearly shown in Fig. 1 the modulating sig nal cm is superimposed on the control signal 60 While actual to produce the final signal e0 which is applied to the terminals 35, 36. These two signals are applied in series so that eozeciem. Refer now to Fig. 3. Herein I show in somewhat schematic manner the production of the final signal e0 for one complete time cycle of cam 6|. Although of alternating current, I have assumed that the unbalance voltage ec has a uniform effective value of X above zero value base line. The full cycle of growth and decay in value of cm is shown in solid line. The resultant signal eo eciem is shown dotted. For the examples given, the ratio of on-time to off-time of the heater [3 is about .43.

As previously mentioned, the voltage on at terminals 35, 36 is impressed between the grid 4|] and cathode 4| of triode 38, whose plate voltage is of supply phase. The relation of the two voltages as to phase and magnitude controls the D.-C. voltage E1 which is to be compared to E2. When the signal voltage e0 is out of phase with the plate voltage of triode 38, the plate current is reduced and E1 becomes less in comparison with E2. This reduces the negative voltage applied to the grid of thyratron 45, completing the circuit to energize relay 49 and turning on the resistor (heat) l3. Thus the out-of-phase" time of signal e0 is the on time of supplying heat to the furnace 6. Obviously the arrangement could be reversed if desired.

The maximum value Z (Fig. 3) of em may be varied by manually moving the contact along resistance Sb to pick off a, desired portion of the unbalance in conductor 65. The magnitude of the proportioning band depends on the maximum value of em and so can be adjusted simply by means of the Sb potentiometer. The ratio of the in-phase to the out-of-phase signal 8m (V/W in Fig. 3) may be readily and accurately adjusted by moving the contact 65 along the resistance Sp.

In Fig. 2 I have shown the boundary of the voltage envelope as comprising straight lines, a result which would be produced if the cam 6| is shaped to have a uniform rise and fall, thus providing a linear relation between movement and voltage. Under the same conditions the curves of Fig. 3 are straight lines. It will be appreciated that if the cam BI is an off-center disk or eccentric, the relation will be sinusoidal and the boundary of the envelope of Fig. 2 as well as the em and en curves of Fig. 3 will emulate wave forms. I indicate here no distinct preference in the shape of cam 6| but believe that this may well be chosen differently for different types of processes and systems to be controlled. It is my contemplation that the cam 6| may be so shaped as to develop a desirable outline for the envelope of Fig. 2 and for the curves of Fig. 3. This provides one of the adjustable features of my invention along with possible variation in speed of rotation of the cam 6|, as well as the possibility of providmg said cam with a number of lobes of desired shape.

In Fig. 4 I show a modification of a part only of the complete circuit of Fig. 1. Inasmuch as this particular modification encompasses a variation only in the method of establishing a modulating signal an it does not appear necessary to duplicate the measuring and controlling circuits of Fig. 1. It appears sufficient to describe how I propose to apply to the terminals 35, 36 a signal at which is a composite of the signals 6c and 'em where'the latter is cyclically produced in a manner somewhat different than is shown in Fig. 1.

' In this modification the reciprocating magnetic core 58 is replaced by a resistance bridge modulator comprising a 360 slidewire 61 tapped at two points 180 apart. The contact arm is driven by a synchronous motor 62 and moves at a uniform rate along the slidewire 61, alternately unbalancing the modulating bridge 68 in one direction or the other. The unbalance voltage em provides an envelope having the characteristics of Figs. 2A and 3 with one complete cycle per revolution of the contact 66 over the slidewire 61.

This modification has certain advantages and certain disadvantages over that of Fig. It can be made into a very compact unit which can be located at will. On the other hand, it has the disadvantage of a sliding open contact as compared to the inductive coupling of Fig. 1. If the slidewire 61 is accurately wound for linearity, the timing of the device will be a very accurate function of the position of the adjusting slidewire Sb. This may be used to accurately control the average rate of change of some controlled variable as illustrated in Fig. 5 which will now be explained.

Certain elements of Fig. 5 are the same as those of Figs. 1 and 4 and bear the same reference numerals. A modulator 68 includes the potentiometer Sm having a continuous slidewire 61 tapped at two points 180 apart and a contact arm 66 synchronously rotated around the slidewire 6'! through the agency of a motor 62. The adjustable potentiometer Sp is provided with an index 69 which may be graduated in terms of rate. As previously explained, the signal em produced by the modulator bridge 68 fits an envelope such as shown in Fig. 2A of linear growth and decay of voltage first forward-phase and then reverse-phase. When the potentiometer Sp is at neutral, the ratio of forward-phase to reverse-phase is .50. Movement of the adjustment Sp will vary the ratio of forward-phase to reverse-phase signal em.

The signal em is applied to an electronic relay 26A similar to the relay 26 of Fig. 1, but provided with a normally open contact 49A and a normally closed contact 49B. The contacts 49A, 49B are connected through a two-position switch 10 to control direction of rotation of a capacitor-run motor H having windings 12 and 73, as well as a capacitor 14. A common terminal of the windings I2, 13 is joined by a conductor 15 in series through limit switches 16, 11 to one side of a power source 18.

The control bridge producing the unbalance signal 6c includes the control potentiometer Sc adjusted by the motor 9 along with the measuring potentiometer 1, 8. The standard potentiometer SS includes the resistance and a contact arm 29, the latter adapted to be positioned by the motor II through the agency of a friction drive 19 in such manner that the contact arm 29 may be manually moved through the friction drive I9 relative to the motor H. The arm 29 has a proper extension adapted to engage the limit switches 16, 11 which are individually mounted in an adjustable manner upon a track 80 which encircles the slide-wire 30. The arrangement is such that the limit switches 16, I! may be separately; manually positioned along the track 80 to define the limits of travel of the contact arm 29 along the slidewire 30. Due to the friction drive 19, the'motor 1| may cause the arm 29 to engage either of the limit switches 16 or II and thereafterxto not stall or damage the motor H. The arrangement described. provides a means for smoothly and uniformly varying the standard to which the control system is to operate. This is accomplished by a smooth continuous movement of the arm 29 along the slidewire 30 whereby the value SS is continuously varied and at a rate dependent upon the proportion of the time that motor H is operating in one direction, i. e. depending upon the signal em.

In Fig. 5 I have disclosed a ready means for controlling in accordance with a preselected rate of change in the variable, and to maintain the variable at such a preselected rate of change in either an increasing or a decreasing manner. I have provided a ready means for adjustably varying both ordinates of the plot of the variable against time, namely, an adjustment of the extreme values of the variable and of the slope of the increase or decrease. I have further provided ready means for reversing the trend of control at the previous rate or for thereafter manually varying the rate as desired. Inasmuch as certain particular features disclosed herein in Fig. 5 are disclosed in my parent Patent No. 2,495,844 and are also disclosed and claimed in my divisional Patent No. 2,593,562, it appears unnecessary to here go into a further detailed explanation of the showin of Fig. 5.

In Fig. 6 I show a modification of the arrangement of Fig. 5. The arrangement is such asto provide the possibility of automatically performing a complete control cycle or of selectively utilizing hand control. Fig. 6 shows the complete circuit intermediate the measuring slidewire I, 8 ald the output signal supplied to terminals 35, 3

I show the modulator bridge 68 (producing the signal em) as having a rate of increase p0,- tentiometer RI and rate of decrease potentiometer RD in addition to the synchronously driven potentiometer Sm. The potentiometers RI and RD are selectively included in the bridge circuit 68 by a contact arm I01 engaging either contact I or contact D in the alternate positions of a relay RA. The potentiometers RI and RD respectively refer to and preset the rate of increase or rate of decrease of the variable, namely, in this case temperature. These potentiometers RI and RD are hand adjusted with reference to graduated scales bearing the same titles.

The premis used is that the control is operating in an increasing temperature direction and with arm I01 contacting at the point I with the relay RA deenergized. This predicts that the modulator bridge 68 includes the elements RI and Sm but does not include the element RD. The output of bridge 68, namely, signal em, produces a forward-phase and a reverse-phase signal similar to that shown as a voltage envelope in Fig. 2A.

The signal 6m is applied to an electronic relay ER! having a normally closed contact H18, which is connected directly across the conductors I09, III] of the motor 'H. The contact I08 parallels the motor capacitor M and a resistance III, for shorting out the same (when closed) and plugging the motor. Direction of rotation of motor H is either clockwise or counterclockwise, dependent upon whether the contact arm H2 of the relay RA engages CCW or CW. As shown, the motor is connected for CCW rotation during the time portion of the time the contact I68 is open. As previously explained, the proportion of open" to closed time of the contact IE8 is related to the relation of forward-phase to reverse- 11 phase of the signal em. Inasmuch as the motor ll rotates only when the contact tilt is open, and then only in CW or CCW direction, the motor operation differs somewhat from that previously described. Referring to Fig. 7, it will be observed that the progression of slope MN is accomplished by the motor of Fig. 5 as a difference between CW and CCW alternate movements of the motor. In other words, as previously explained, the motor rotates a small amount CW and then a small amount COW alternately, and the progression is by the difierence of said movements, both as to slope (rate) of the line and the direction of preponderance determines the direction of movement. On the other hand, the motor of Fig. 6 moves only in a single direction and inches along by the duration of the em signals which open contact Hi8. Those 8m signals which close contact I33 short the capacitor 74 and plug the motor to a stop. Direction of rotation is controlled entirely by the position of the contact arm I I2 engaging either CCW or CW. In the example being described in connection with Fig. 6, the motor H is rotating CCW at a rate determined by the position of RI and upwardly along the increase line of MN of Fig. 7.

In Fig. 8 I show a modification of Fig. 1 wherein a single modulator may serve a plurality of controllers. In view of the explanation of Fig. 1, it seems unnecessary to go into detail as the circuit of Fig. 8.

It will be appreciated from the above detailed description that my invention has wide application and is not limited to the specific examples illustrated and explained. While I have described a single embodiment comprising the control of an electric furnace, it will be appreciated that the invention is equally applicable to fuel fired furnaces or in fact to the control of other variables than temperature.

The present application is a division of my copending parent application 5. N. 674,752 filed June 6, 1946, now Patent 2,495,344, granted J anuary 31, 1950. Figs. 1, 2, 3, 4, 6, 7 and 8 of this application are copies of Figs. 1, 2, 3, l, 9, 12 and 13 respectively of said parent application.

References may also be made to my copending application S. N. 68,027 filed December 29, 1948, as a division (now Patent No. 2,593,562) of the said parent application S. N. 674,752. Figs. 2A and 5 of the present application are duplicates of Figs. 2 and 1 respectively of said divisional application 63,027. Fig. 5 herein includes the disclosure of Fig. 5 of said parent application.

What I claim, and desire to secure by Letters Patent of the United States, is:

1. Signal generating means for cycling control systems comprising in combination, a bridge network including a pair of electric elements providing control means for the bridge output, a source of alternating current for the bridge, a movable member positionable relative to and cooperating with said elements to energize the bridge from said source with a potential smoothly growing and decaying alternately in opposite phases when the member is positioned cyclically relative to the elements, a potentiometer resistor connected in shunt to said elements, a slider on said potentiometer resistor, an output signal circuit extending from said slider and from a selected potential point on said elements, and motive means arranged to position the movable member cyclically at a uniform. rate relative to the elements.

2, Signal generating means for cycling control systems comprising-in combination, a bridge network including a pair of electric elements providing control means for the bridge output, a source of alternating current for the bridge, a movable member positionable relative to and cooperating with said elements to energize the bridge from said source with a potential smoothly growing and decaying alternately in opposite phases when the member is positioned cyclically relative to the elements, a potentiometer resistor connected in shunt to said elements, a slider on said potentiometer resistor, a conductor .joining said slider and a selected potential point on said elements, a second resistor in said conductor, .a second slider adjustable over the second resistor, and output signal circuit extending from one end of the second resistor and from the second slider, and motive means arranged to position the movable member cyclically at a uniform rate relative the elements.

3. The combination of claim 1 wherein the electric elements are electrically symmetrical.

4. The combination of claim 1 wherein the slider is hand adjustable to preselect the ratio of bridge energization at one phase to that at the other phase in a given time.

5. Signal generating means for cycling control systems comprising in combination, a bridge including a 360 slidewire, a source of A.-C. connected to said bridge and Wire at points 180 apart, a slider movable at uniform rate over said wire, motive means, positioning the slider cyclically over said wire, a potentiometer bridging said source, a slider on said potentiometer, and a signal circuit extending from said sliders.

6. Signal generating means for cycling control systems comprising in combination, a bridge including a 360 slidewire, a source of A.-C. connected to said bridge and wire at points 180 apart, a slider movable at uniform rate over said wire, motive means positioning the slider cyclically over said wire, a potentiometer bridging said source, a slider on said potentiometer, a conductor joining said sliders, a resistor in said conductor, a third slider adjustable over the re,- sistor, and a signal circuit e2- ending from said third slider and from one, end of the resistor.

7. Signal generating means for cycling an on and off control system including in combination, a pair of like secondary windings, a resistor, means connecting said windings and resistorin a closed series circuit, a slider on said resistor, an output circuit extending from the slider to a point between said windings, an A.-C. energized primary symmetrically disposed in relation to the secondaries, a core movable relative to said primary to oppositely vary the inductive relation of the secondaries to the primary, and means to oscillate said core through itspath periodically at a uniform rate from a position inducing zero potential in the secondaries to maximum of one phase to zero to maximum in opposite phase repeatedly.

8. Signal generating meansfor cycling .an on and off control system including in combination, a movable core transformer having a pair of like secondary windings, an A.-C. energized primary for the secondaries, aresistor, means connecting said windings and resistor in aclosed series circuit, a slider on said resistor, asecond circuit extending from the slider to a point between said windings, a core cyclically movable relative to the primary andsecondary windings for inductively coupling them, and motive meanstomove the core at a uniform rate from a posi- ANTHONY J. HORNFEC'K.

REFERENCES CITED 7 The following references are of record in the file of this patent:

5 UNITED STATES PATENTS Number Name Date 1,764,347 Pullwitt June 17, 1930 2,432,422 Hornfeck Dec. 9, 1947 2,491,606 Dickey et a1. Dec. 20, 1949 

